A relationship is more than the sum of its partners. It operates as a system, where each person affects the other in complex ways. If your partner comes alone, the dynamic between the two of you will change anyway, so your best chance to get what you want is by participating.
The need to “fix” one person implies a judgment as to what is correct or proper, and I do not provide that. In fact, very often that sort of judgment itself is at the heart of the relationship problem. My view is that there can be many ways for couples to get along, and I help negotiate a viable relationship for both of you.
I hold to these principles about couples therapy (Margolin, 1982):
If it is really true that your partner is the one with the primary difficulty, it is also quite possible that, even with the best intent, you are having your own struggle supporting them in getting to what they need. It has been said that the purpose of a relationship is for people to support one another. You may not subscribe to this idea, but your partner probably does. Ignoring their immediate “problem” is unlikely to lead to a satisfactory relationship for you.
Even if you only attend to clear yourself of blame, you will likely discover opportunities to be more meaningfully helpful to the person you share your life with, and thus improve things for both of you.